You could indeed work around this using eval:
earliest=-10m@m latest=@m *base_search* | addinfo | eval min_time = info_min_time | bucket span=2m info_min_time | eval info_min_time = strftime(info_min_time, "%H:%M:%S")| eval offset = min_time - info_min_time | eval _time=_time-offset | bucket span=2m _time | eval _time=_time+offset| stats xxx by _time
This is the search I used for testing my work:
sourcetype=access_combined earliest=-9m@m | addinfo | eval orig_time = strftime(_time, "%H:%M:%S")| eval min_time = info_min_time | bucket span=2m info_min_time | eval offset = min_time - info_min_time | eval _time=_time-offset| bucket span=2m _time | eval _time=_time+offset | eval min_time = strftime(min_time, "%H:%M:%S") | eval info_min_time = strftime(info_min_time, "%H:%M:%S")| table min_time info_min_time _time orig_time
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